Tower erecting system

ABSTRACT

In certain embodiments, a tower lifting system comprises a primary lifting system and a secondary lifting system. The primary lifting system includes a lift cap configured to support a tower section to be lifted, the lift cap having a first plurality of hoists, and a lift pole coupled to the lift cap, the lift pole having a lifting mechanism configured to lift the lift cap, the lift pole, and the tower section to be lifted from within a previously lifted tower section. The secondary lifting system comprises a second plurality of hoists configured to raise the tower section to be lifted to the lift cap from a tower foundation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. patentapplication Ser. No. 13/720,535, entitled “Tower Erecting System,” filedDec. 19, 2012, which is a Non-Provisional U.S. Patent Application ofU.S. Provisional Application No. 61/589,170, entitled “Tower ErectingSystem,” filed Jan. 20, 2012, both of which are herein incorporated byreference in their entireties.

BACKGROUND

The invention relates generally to wind energy systems, and, moreparticularly, to a system and method for constructing a wind energytower system.

Towers for wind energy systems exist in several forms. Generally, a windtower includes a tower structure with a wind turbine affixed at the topof the tower structure. Thus, as the wind tower height increases, thewind turbine is placed at higher altitudes. Generally, wind velocity andconsistency increase with altitude. As a result, a wind turbine canoften produce more electrical energy, and more consistently, and thusgenerate more income, when placed at a higher altitude. However, thecost of these wind towers increases as the wind tower height increases.Moreover, for some tower types, the tower, transportation, andconstruction costs increase with tower height at a faster rate than theadditional income generating potential. Therefore, at some tower height,the increasing cost of the tower is such that the net revenue from thegenerated electrical energy begins to decrease with increasing towerheight. Additionally, for some tower types, there may be constructionequipment limitations, such as crane height. That is, the height of thetower may be limited by the height of the crane used to construct thetower. Unfortunately, these constraints limit the practical altitude ofwind turbines.

BRIEF DESCRIPTION

In an exemplary embodiment, a tower lifting system comprises a primarylifting system and a secondary lifting system. The primary liftingsystem includes a lift cap configured to support a tower section to belifted, the lift cap having a first plurality of hoists, and a lift polecoupled to the lift cap, the lift pole having a lifting mechanismconfigured to lift the lift cap, the lift pole, and the tower section tobe lifted from within a previously lifted tower section. The secondarylifting system comprises a second plurality of hoists configured toraise the tower section to be lifted to the lift cap from a towerfoundation.

In another exemplary embodiment, a tower lifting system comprises asecondary lifting system configured to raise a tower section of amulti-section tower to a lifting position and a primary lifting systemconfigured to raise the tower section and the secondary and primarylifting systems to an assembled position.

In a further embodiment, a method for erecting a tower includes nestingfrusto-conical tower sections within one another and within afrusto-conical tower base and securing the frusto-conical tower base toa tower foundation. The method further includes lifting eachfrusto-conical tower section from within the frusto-conical tower basewith a lifting apparatus and securing each frusto-conical tower sectionto the frusto-conical tower base or to a previously liftedfrusto-conical tower section.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a diagrammatical representation of a wind power system;

FIG. 2A is a diagrammatical representation of a partially constructedwind tower having frusto-conical tower sections;

FIG. 2B is a diagrammatical representation of a partially constructedwind tower having frusto-conical tower sections;

FIG. 2C is a diagrammatical representation of a partially constructedwind tower having frusto-conical tower sections;

FIG. 3 is a perspective view of unassembled frusto-conical towersections resting on a tower foundation in a nested arrangement;

FIG. 4 is a schematic of an embodiment of a lifting apparatus for a windtower, illustrating a lift cap and a secondary lifting system of thelifting apparatus;

FIG. 5 is a schematic of an embodiment of the lifting apparatus for awind tower, illustrating a lift cap and a primary lifting system of thelifting apparatus;

FIG. 6 is a partial cross-sectional view of an interior of a towersection, illustrating lifting lugs of the tower section;

FIG. 7 is a partial cross-sectional side view, taken along line 7-7 ofFIG. 5, illustrating two lap welds joining two tower sections;

FIG. 8 is a schematic of a completed wind tower having frusto-conicaltower sections;

FIG. 9 is a schematic of an embodiment of the lifting apparatus for awind tower, illustrating a rack and pinion lifting system;

FIG. 10 is a schematic of an embodiment of the lifting apparatus for awind tower, illustrating a floatation lifting system;

FIG. 11A is a cross-sectional view of an embodiment of the towersections having a corrugated or fluted cross section;

FIG. 11B is a perspective view of an embodiment of the tower sectionshaving a corrugated or fluted cross section;

FIG. 12A is a cross-sectional view of an embodiment of the towersections having a corrugated or fluted cross section;

FIG. 12B is a partial perspective view of an embodiment of the towersections having a corrugated or fluted cross section; and

FIG. 13 is a cross-sectional view of an embodiment of the tower sectionshaving a polygonal cross section.

DETAILED DESCRIPTION

The present disclosure describes a tower which can support large windturbines, or other heavy components, and a system and method forerecting such a tower without the need for a large external liftingsystem, such as a crane. In certain embodiments, the tower includesmultiple frusto-conical tower sections which, when lifted from withinone another, fit together with a very tight clearance. Specifically, abottom portion of the tower section being lifted overlaps within a topportion of a previously lifted tower section. In other words, theoutside diameter and shape of the bottom portion of the tower sectionbeing lifted is designed to match the inside diameter and shape of thetop portion of the previously erected tower section. The two towersections mate with a small overlap, where there is essentially zeroclearance between the outside surface of the upper tower section and theinside surface of the tower section below it. The two tower sections maybe welded together at the top of the overlap and the bottom of theoverlap.

As discussed in detail below, prior to the tower erection process, thetower sections are nested inside one another at the base of the tower. Alifting apparatus is used to individually lift each of the towersections into place. Specifically, a primary lifting system is locatedinside the tower section being lifted and may extend at least one towersection length below the bottom of the tower section being lifted. Theprimary lifting system lifts the tower section and the entire liftingapparatus until the tower section emerges out of the top of thepreviously erected tower section. The primary lifting system holds thetower section in place while the tower section is secured (e.g., welded)to the tower section previously lifted. Once the tower section is weldedin place, a secondary lifting system of the lifting apparatus raises thenext tower section from its resting place at the base of the tower andholds the next tower section. Thereafter, the primary lifting systemlifts the next tower section, which is being held by the secondarylifting system, and the entire lifting apparatus until the next towersection is in place for welding.

Turning now to the drawings, FIG. 1 is a diagrammatical representationof a wind power system 10 including a wind tower 12 which may be erectedusing a lifting apparatus. The wind tower 12 supports a wind turbine 14configured to convert wind energy into electrical energy. In theillustrated embodiment, the wind turbine 14 is a horizontal axis windturbine, but, in other embodiments, the wind turbine 14 may be avertical axis wind turbine. The wind turbine 14 includes a rotor 16coupled to a nacelle 18, which houses a generator 20. The rotor 16includes a hub 22 and blades 24 which convert the wind energy into lowspeed rotational energy. Specifically, as wind 26 blows past the blades24, the blades 24, and therefore the hub 22, are driven into rotation.The rotor 16 is further coupled to a low speed shaft 28 within thenacelle 18. The low speed shaft 28 is coupled to a gear box 30 whichconverts the low speed rotation of the low speed shaft 28 into a highspeed rotation suitable for generating electricity. Specifically, thegear box 30 transfers the rotational energy of the low speed shaft 28 toa high speed shaft 32. The high speed shaft 32 is further coupled to thegenerator 20, which converts the rotational energy into electricalenergy. In other embodiments, the wind turbine 14 may include othercomponents such as a direct drive or multiple generators 20.

In certain embodiments, the wind power system 10 may have an inverter34. Specifically, the electricity generated by the generator 20 may berouted to an inverter 34 coupled to the wind tower 12. The inverter 34converts the electricity from direct current (DC) to alternating current(AC). From the inverter 34, the electricity is supplied to a power grid36. From the power grid 36, the electricity may be distributed to homes,buildings, and other consumers of electricity.

In the illustrated embodiment, the wind tower 12 has a height 38.Additionally, the wind tower 12 is constructed from multiple towersections 40. Each tower section 40 has a frusto-conical shape. Asdiscussed in detail below, the wind tower 12 may be erected by liftingthe tower sections 40 from within one another. More specifically, alifting apparatus is used to individually lift each tower section 40 andhold the tower section 40 in place while the tower section 40 is secured(e.g., welded) to the previously erected tower section 40 below it. Incertain embodiments, the wind tower 12 may include approximately 3 to 40tower sections 40. Furthermore, the tower sections 40 each have a height42, which may be approximately 40 to 100 feet or more. Consequently, theheight 38 of the wind tower 12 may be approximately 150 to 1500 feet ormore. Furthermore, as the height 38 of the wind tower 12 increases, thediameter of the tower sections 40 may increase, thereby increasing theload capacity of the wind tower 12. As a result, the wind tower 12 maybe capable of supporting a nacelle 18 having a larger generator 20, suchas a 1-10 million watt generator 20.

FIGS. 2A-2C are schematics of the wind tower 12 in various stages ofassembly, illustrating the joints between the tower sections 40. Asmentioned above, the wind tower 12 includes multiple tower sections 40,each tower section 40 having a frusto-conical, hollow shape. FIG. 2Aillustrates a first tower section 44 which serves as the base of thewind tower 12. As shown, the first tower section 44 rests on afoundation 46 of the wind tower 12. In certain embodiments, thefoundation 46 may be formed from concrete. The first tower section 44 isrigidly attached to the foundation 46 by a foundation anchor method. Forexample, the first tower section 44 may be secured to the foundation 46with a composite material. The composite material may include a rock andgravel aggregate mixed with a polymer based matrix material. In such anembodiment, a recess in the foundation 46 allows the first tower section44 to rest partially below a top 48 of the foundation 46. The compositematerial is used to fill the recess, thereby surrounding and bonding thefirst tower section 44 to the foundation 46. In another embodiment, thefirst tower section 44 may be bolted to the foundation 46. Specifically,the first tower section 44 may have a ring welded to a bottom of thefirst tower section 44. The ring may have holes spaced around thecircumference of the ring. The locations of the holes are such thatbolts affixed to, and protruding from, the foundation 46 are received bythe holes. With the bolts of the foundation 46 extending through theholes of the ring, nuts are placed onto the end of the bolts and aretightened down, thereby rigidly securing the first tower section 44 tothe foundation 46.

FIG. 2B illustrates a second tower section 50 assembled and secured tothe first tower section 44. As discussed above, each tower section has afrusto-conical, hollow shape. As a result, the tower sections 40 may bedesigned to fit together with a very tight clearance. Specifically, theoutside diameter and shape of the bottom portion of the tower section 40being lifted is designed to match the inside diameter and shape of thetop portion of the previously erected tower section 40. In theillustrated embodiment, the second tower section 50 is lifted fromwithin the first tower section 44 in a direction 52. In certainembodiments, the second tower section 50 may be lifted by a crane orother external lifting apparatus. As indicated by reference numeral 54,a bottom portion 56 of the second tower section 50 and a top portion 58of the first tower section 44 fit together with a very tight clearanceto create an overlap 60. In other words, the bottom portion 56 of thesecond tower section 50 remains inside the first tower section 44. Withthe second tower section 50 lifted in the final erected position, twolap welds are completed. A first lap weld is completed along the topportion 58 of the first tower section 44, thereby joining the topportion 58 to the outside of the second tower section 50. A second lapweld is made along the bottom portion 56 of the second tower section 50,thereby joining the bottom portion 56 to the inside of the first towersection 44.

FIG. 2C illustrates a third tower section 60 assembled and secured tothe second tower section 50. As similarly discussed above, the thirdtower section 60 is lifted from within the first and second towersections 44 and 50 in the direction 52. The frusto-conical, hollow shapeof the second and third tower sections 50 and 60 enables a bottomportion 62 of the third tower section 60 to overlap with a top portion64 of the second tower section 50 to create an overlap 66. In the mannerdiscussed above, two lap welds are completed to secure the second andthird tower sections 50 and 60. As will be appreciated, the wind tower12 erection process described above is repeated for all tower sections40 of the wind tower 12. The discussion below describes a liftingapparatus which may be used to complete this erection process withoutthe need for a large external lifting system, such as a crane.

FIG. 3 illustrates a nested arrangement of tower sections 40, prior tothe beginning of the wind tower 12 erection process. As mentioned above,prior to the erection process, the tower sections 40 are placed onto thefoundation 46 at ground level. More specifically, the tower sections 40are “nested” inside one another. In other words, each tower section 40is placed outside of the next smallest tower section 40. In theillustrated embodiment, the tower sections have sides 68 which have around cross-section. However, in other embodiments, the sides 68 of thetower sections 40 may have a polygonal, circular, oval, corrugated, orfluted cross-section, as described in greater detail below with respectto FIGS. 11-13.

FIG. 4 is a schematic of an embodiment of a lifting apparatus 70 for thewind tower 12, illustrating a lift cap 72 and a secondary lifting system74 of the lifting apparatus 70. In order to stabilize the liftingapparatus 70 and the tower section 40 being lifted, the liftingapparatus 70 includes the lift cap 72. Specifically, the lift cap 72 isplaced on top of the nested tower sections 40 before the erectingprocess begins. Alternatively, in certain embodiments, the first severaltower sections 40 may be lifted and secured (e.g., welded) using aconventional crane. In such an embodiment, the lift cap 72 may be placedon the top of the most recently lifted tower section 40 before thelifting apparatus 70 is used. During the erecting process, the lift cap72 is coupled to the tower section 40 currently being lifted.Additionally, the nacelle 18, which houses the generator 20 and othercomponents of the wind turbine 14, is placed on top of, and is attachedto, the lift cap 72. In this manner, as the lifting apparatus 70 liftseach tower section 40, the lifting apparatus also raises the lift cap 72and the nacelle 18 of the wind turbine 14.

Each tower section 40 to be lifted is first raised from its restingposition on the foundation 46 at the base of the wind tower 12.Specifically, the secondary lifting system 74 includes hoists 76 whichraise the tower section 40 with cables 78. For example, the hoists 76may be electric or hydraulic winches. The tower section 40 to be liftedis raised in the direction 80 until the tower section 40 is against thebottom of the lift cap 72. Once the tower section 40 has been raised upto the lift cap 72, the tower section 40 is coupled to the lift cap 72using lugs and pins. For the duration of the lift and welding sequence,the tower section 40 is held in this position against the lift cap 72.As discussed in detail below, once the tower section 40 to be lifted israised by the secondary lifting system 74 and coupled to the lift cap72, a primary lifting system is used to lift the tower section 40, thelift cap 72, and the nacelle 18.

While the tower section 40 is being lifted into place by the primarylifting system, the tower section 40 may be subjected to undesiredmovement due to wind and other loads. To help reduce undesired lateralmovement of the tower section 40 during the lifting and weldingsequence, the lift cap 72 includes guide arms 82 which extend down aportion of the wind tower 12 that has already been erected and welded.For example, in certain embodiments, the lift cap 72 may include aplurality of structural members, such as I-beams, that extend from oneside of the tower section 40 to the opposite side of the tower section40, with each end of the structural members coupled to a respectiveguide arm 82. As such, because the guide arms 82 are positioned onopposite sides of the tower section 40, they generally pull against eachother and maintain forces evenly amongst the opposite sides. Any evennumber of opposite guide arms 82 may be used. For example, in certainembodiments, six or twelve opposite guide arms 82 may be used. Ingeneral, the number of guide arms 82 may depend on the specificconfiguration of the tower 12 being erected.

The guide arms 82 rest against the erected and welded portion of thewind tower 12, thereby preventing horizontal motion of the guide arms82, the lift cap 72, and the tower section 40 coupled to the lift cap72. Additionally, each guide arm 82 includes a guide mechanism 84 whichprovides for relative vertical motion of the guide arms 82 and the liftcap 72 with respect to the welded portion of the wind tower 12. Forexample, the guide mechanism 84 may include wheels 86, as shown, a trackmechanism, or other mechanism configured to allow vertical motion of theguide arms 82 with respect to the erected portion of the wind tower 12.

FIG. 5 is a schematic of an embodiment of the lifting apparatus 70 forthe wind tower 12, illustrating the lift cap 72 and a primary liftingsystem 88 of the lifting apparatus 70. In the illustrated embodiment,the primary lifting system 88 comprises a cable lift system 90. Asdiscussed in detail below, the cable lift system 90 operates to push thelift cap 72 upwards, in a direction 92, thereby lifting the nacelle 18on top of the lift cap 72 and the tower section 40 which is held againstthe bottom of the lift cap 72. In the illustrated embodiment, a towersection 94 that has been lifted by the secondary lifting system 74 iscoupled to the bottom of the lift cap 72 by lugs 96 and bolts 98. Thecable lift system 90 continues to lift the lift cap 72, the nacelle 18,and the tower section 94 until the outside of a bottom portion 100 ofthe tower section 94 is up against the inside of a top portion 102 ofthe previously erected tower section 40. Once the tower section 94 is inplace, the bottom portion 100 of the tower section 94 and the topportion 102 of the previously erected tower section 40 are weldedtogether using a double lap joint.

The cable lift system 90 includes a lift pole 104. In certainembodiments, the lift pole 104 may be approximately twice as long inlength as the tower sections 40. For example, the lift pole 104 may beapproximately 60, 70, 80, 90, 100, or more feet in length. Due to thelength of the lift pole 104 being greater than the length of a singletower section 40, the first single or several tower sections 40 may belifted and held in place for welding by a conventional crane or otherexternal lifting apparatus, as discussed above. Similarly, while theillustrated embodiment does not show the blades 24 of the rotor 16coupled to the hub 22, the blades 24 may also be raised and attached tothe hub 22 with a conventional crane or other external liftingapparatus. For example, in certain embodiments, the blades 24 may beraised and attached to the hub 22 after 2, 3, 4, or 5 tower sections 40have been lifted and welded in place.

Once the tower section 94 is coupled to the lift cap 72, cables 106 arecoupled to lifting lugs 108 located at the bottom of the previouslyerected tower section 40. The cables 106 are then directed down to lowerpulleys 110 at the bottom of the lift pole 104. The cables 106 arerouted upwards to upper pulleys 112 at the top of the lift pole 104 andare then connected to hoists 114. In the illustrated embodiment, thehoists 114 are disposed on the outside of the arms 82 of the lift cap72. In other embodiments, the hoists 114 may be located on the inside ofthe arms 82 or on another portion of the lift cap 72. For example, thehoists 114 may be electric or hydraulic winches. Moreover, the cablelift system 90 may include 3 to 20 hoists 114, with each hoist 114connected to a respective cable 106. Once the cables 106 are connectedto the hoists 114, the cables 106 are pulled by the hoists 114 (i.e.,reeled in) until tight, at which point the lift pole 104, the lift cap72, the nacelle 18, and the tower section 94 are supported by the cables106. In this manner, the hoists 114 and the cables 106 raise the liftpole 104, the lift cap 72, the nacelle 18, and the tower section 94 inthe direction 92.

The lifting apparatus 70 further includes a control system 116 coupledto the hoists 114 and coupled to a leveling sensor 118. As shown, theleveling sensor 118 is coupled to the lift cap 72. Certain embodimentsmay include multiple leveling sensors 118. The leveling sensor 118 isconfigured to monitor an angle of the lift cap 72. More specifically,the leveling sensor 118 monitors whether the lift cap 72 is level ortilted. Using feedback from the leveling sensor 118, the control system116 coordinates the rate of pull of the hoists 114 to lift the towersection 94 and the nacelle 18. Specifically, the control system 116operates the hoists 114 to reel in the cables 106 to lift the lift pole104, thereby raising the nacelle 18 and the tower section 94. As will beappreciated, the weight and position of the generator 20 within thenacelle 18 may cause an uneven weight distribution on the lift cap 72.As a result, some hoists 114 may need to have a greater lifting capacitythan other hoists 114, depending on the location of the respective hoist114 relative to the generator 20. Additionally, as the hoists 114 reelin the cables 106, the uneven weight distribution may cause the certainhoists 114 to reel in cables faster than others. The leveling sensor 118detects the uneven raising of the lift cap 72 and communicates theunevenness to the control system 116. In response, the control system116 sends control signals to some or all of the hoists 114 to adjust theoperation of each hoist 114 accordingly. For example, the control system116 may stop the operation of some hoists 114 while continuing theoperation of other hoists 114, as necessary, to bring the lift cap 72back to a level orientation.

As mentioned above, the lift pole 104 may have a length approximatelytwice the length of the tower section 40. As will be appreciated, as thecables 106 are reeled in by the hoists 114, an angle 120 formed by eachcable 106 extending from the lifting lugs 108, around the lower pulleys110, and up to the upper pulleys 112 will increase. However, the angle120 may be reduced by increasing the length of the lift pole 104. Forexample, during the lifting process with a lift pole 104 having a lengthapproximately twice as great as the length of the tower section 94, theangle 120 may not increase beyond 15, 20, 25, or 30 degrees. As aresult, the force applied to the lifting lugs 108 by the cables 106 inthe horizontal direction as the cables 106 are reeled in by the hoists114 may be reduced.

FIG. 6 is a partial cross-sectional view of an interior surface 122 of atower section 40, illustrating lifting lugs 108 of the tower section 40.As mentioned above, the cables 106 used to lift the lift pole 104, thelift cap 72, and the individual tower sections 40 are connected tolifting lugs 108. Each lifting lug 108 extends generally perpendicularlyfrom the interior surface 122 of the tower section 40 and has anaperture 124 through which the respective cable 106 is inserted andsecured to the lifting lug 108. In certain embodiments, the lifting lugs108 may be formed from steel and may be welded to the interior surface122 of the tower section 40. As will be appreciated, each tower section40 may have at least as many lifting lugs 108 as cables 106 used in thecable lift system 90.

FIG. 7 is a partial cross-sectional side view, taken along line 7-7 ofFIG. 5, of an upper tower section 128 and a lower tower section 130,illustrating two lap welds 132 joining the upper tower section 128(i.e., the tower section 40 being lifted) and the lower tower section130 (i.e., the previously erected tower section 40). Once the primarylifting system 88, e.g., the cable lift system 90, has raised the uppersection 128 such that the bottom portion of the upper tower section 128has contacted the top portion of the lower tower section 130, the twotower sections 128 and 130 are joined with two lap welds 132.Specifically, an inner lap weld 134 and an outer lap weld 136 arecreated between the two tower sections 128 and 130. In certainembodiments, the outer lap weld 136 is completed first, and the innerlap weld 134 is completed second. As shown, the inner lap weld 134 ismade along a bottom edge 138 of the upper tower section 128 and joiningto an inside surface 140 of the lower tower section 130. Similarly, theouter lap weld 136 is made along a top edge 142 of the lower towersection 130 and joining to an outside surface 143 of the upper towersection 128. As will be appreciated, the inner and outer lap welds 134and 136 are completed along the entire circumference of the bottom edge138 of the upper tower section 128 and the top edge 142 of the lowertower section 130, respectively.

FIG. 8 is a schematic of a completed wind tower 12 havingfrusto-conical, hollow tower sections 40. Once each tower section 40 hasbeen lifted by the lifting apparatus 70, the lift cap 72 supporting thenacelle 18 is welded to the top tower section 40, as indicated by arrows144. Additionally, the guide arms 82 of the lift cap 72 are disconnectedfrom the lift cap 72 and lowered down to the base of the wind tower 12.Similarly, the lift pole 104 is lowered to the base of the wind tower12. With the wind tower 12 fully erected and the nacelle 18 in place atthe top of the wind tower 12, the wind tower 12 may be prepared foroperation.

FIG. 9 is a schematic of an embodiment of the lifting apparatus 70 forthe wind tower 12, wherein the primary lifting system 88 comprises arack and pinion lifting system 146. In the illustrated embodiment, thetower section 40 to be lifted is raised up by the secondary liftingsystem 74 and secured to the bottom of the lift cap 72, in the mannerdescribed above. Thereafter, lift poles (i.e., rigid members) 148coupled to the lift cap 72 are rotated outwards and coupled to motorizedpinion drives 150 which are running on rails 152 having gear teeth 154.In operation, the pinion drives 150 engage with the gear teeth 154 onthe rails 152 and drive the rigid members 148 upward, thereby liftingthe lift cap 72, the nacelle 18, and the tower section 40. As with otherembodiments of the lifting apparatus 70 discussed above, the rack andpinion system 146 may also include the control system 116 and theleveling sensor 118. As will be appreciated, using feedback from theleveling sensor 118, the control system 116 may coordinate the rate ofupward motion of the pinion drives 150 on the rails 152 to maintain aneven lifting rate of the lift cap 72, the nacelle 18, and the towersection 40 being lifted.

FIG. 10 is a schematic of an embodiment of the lifting apparatus 70 forthe wind tower 12, wherein the primary lifting system 88 comprises afloatation lifting system 156. The floatation lifting system 156includes a lift pole 158 coupled to the lift cap 72 and to a floatationdevice 160. For example, the floatation device 160 may be a closedcontainer filled with air. Alternatively, the floatation device 160 maybe an open container taller than the tank 162. The floatation device 160is partially surrounded by and disposed within a tank 162 having an opentop 164. The tank 162 is supported by cables 166 that are coupled to thebottom of the tank 162 and the lifting lugs 108 of the previouslyerected tower section 40.

In operation, the tower section 40 to be lifted is raised up by thesecondary lifting system 74 and secured to the bottom of the lift cap72, in the manner described above. The floatation lifting system 156lifts the lift cap 72, the nacelle 18, and the tower section 40 whenwater or other suitable liquid is pumped into the tank 162. The water orliquid creates an upward buoyant force on the floatation device 160,which pushes the lift pole 158, lift cap 72, the nacelle 18, and thetower section 40 upward. In order to maintain an even lifting rate ofthe lift cap 72, cables 168 are coupled to the lift cap 72 and loweredto the tower foundation 46 where the cables 168 are attached to hoists170 secured to the tower foundation 46. More specifically, as water ispumped into the tank 162 and the upward buoyant force of the flotationdevice 160 pushes the lift pole 158 and the lift cap 72 upwards, abalanced tension is maintained in the cables 168 so that the lift cap 72does not tilt, thereby providing a level platform for the nacelle 18. Incertain embodiments, the floatation lifting system 156 may include thecontrol system 116 and the leveling sensor 118. As will be appreciated,using feedback from the leveling sensor 118, the control system 116 maycontrol the operation of the hoists 170 to maintain a balanced tensionbetween the cables 168.

Once the tower section 40 attached to the lift cap 72 is lifted and inplace for welding, the pumping of water into the tank 162 may be stoppedand/or the hoists 170 may hold the cables 168 in place, thereby holdingthe lift cap 72 and the tower section 40 in place. With the lift cap 72and the tower section 40 in place, the tower section 40 is welded to thepreviously erected tower section 40 with two lap welds 126, in themanner described above. After the tower section 40 is welded in place,the next tower section 40 to be lifted may be raised up to the lift cap72 using the secondary lifting system 74. Additionally, a valve 172 ofthe floatation device 160 may be opened and the tank 162 may be raisedup. Specifically, the cables 166 may be coupled to the lifting lugs 108of the previously erected tower section (i.e., the tower section thathas just been welded in place). As the tank 162 is raised, the waterwithin the tank 162 will enter the floatation device 160 through thevalve 172, thereby causing the floatation device 160 to sink to thebottom of the tank 162. Thereafter, the valve 172 is closed and a pump174 within the floatation device 160 may pump the water out of thefloatation device 160 and into the tank 162, as indicated by arrows 176.As the water is pumped out of the floatation device 160 and into thetank 162, the displaced water will create an upward buoyant force on thefloatation device 160, as described above, thereby pushing the lift pole158, lift cap 72, the nacelle 18, and the tower section 40 upward.

As discussed above, embodiments of the present disclosure include alifting apparatus 70 for a wind tower 12. Specifically, the liftingapparatus 70 is configured to erect the wind tower 12 by raisingfrusto-conical, hollow tower sections 40 from within the other assembledtower sections 40. In this manner, the wind tower 12 may be erectedwithout the use of an external lifting apparatus, such as a conventionalcrane. This enables the construction of larger and taller wind towers 12because the erection of the wind tower 12 is not limited by theavailability or height of a crane used to erect the wind tower 12. Forexample, using the lifting apparatus 70, the wind tower 12 may beconstructed and erected to stand approximately 400, 500, 600, 700, 800,900, or more feet high. As a result, the wind turbine 14 located at thetop of the wind tower 12 is placed at a higher altitude where both windvelocity and wind consistency may be higher, thereby enabling the windpower system 10 to generate more electrical energy.

As described above, the sides 68 of the tower sections 40 may have acircular, oval, polygonal, corrugated, or fluted cross-section that bothfacilitates assembly at the site as well as provides added strength tothe tower sections 40. FIG. 13 illustrates a multi-sided cross-sectionof a polygon. A polygon with as many as 20 side sections, may result ina nearly circular cross-section, but can be constructed with individualbends. In other embodiments, the number of side sections may be 3 to 30or more.

FIGS. 11-12 illustrate a tower section 40 having corrugated or flutedsides 68. As illustrated in FIGS. 11A and 11B, the sides 68 include aplurality of alternating convex and concave sections that includerelatively sharp transitions. Unlike the polygonal shape, the bends arenot all in one direction. As illustrated in FIGS. 12A and 12B, the sides68 include a plurality of alternating convex and concave sections thatinclude relatively smooth transitions. As will be appreciated, withrespect to FIGS. 11-12, when adjacent tower sections 40 are assembledtogether, the alternating convex and concave sections of the abuttingsides 68 will be aligned before welding the adjacent tower sections 40together. It should be understood that the corrugated or fluted sides 68illustrated in FIGS. 11-12 are merely exemplary of the types of towersection sides 68 that may be used. Other types of tower section sides 68may be used having different cross sections, such as the polygonal,circular, or oval cross sections mentioned above.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A method for erecting a tower, comprising: nesting frusto-conicaltower sections within one another and within a frusto-conical towerbase; securing the frusto-conical tower base to a tower foundation;lifting each frusto-conical tower section from within the frusto-conicaltower base with a lifting apparatus; and securing each frusto-conicaltower section to the frusto-conical tower base or to a previously liftedfrusto-conical tower section.
 2. The method of claim 1, comprisingsecuring a nacelle having a wind turbine to the lifting apparatus. 3.The method of claim 1, comprising monitoring an angle of the liftingapparatus with a leveling sensor, and adjusting an angle of the liftingapparatus with a control system coupled to the leveling sensor and thelifting apparatus based upon feedback from the leveling sensor.
 4. Themethod of claim 3, wherein adjusting the angle of the lifting apparatuswith the control system comprises regulating operation of at least onehoist of the lifting apparatus.
 5. The method of claim 1, wherein thelifting apparatus comprises a secondary lifting system configured toraise each frusto-conical tower section to a lifting position, and aprimary lifting system configured to raise each frusto-conical towersection and the lifting apparatus into an assembled position.
 6. Themethod of claim 5, comprising raising each frusto-conical tower sectionto the lifting position with a plurality of hoists of the secondarylifting system.
 7. The method of claim 5, comprising raising eachfrusto-conical tower section and the lifting apparatus into theassembled position with a lift pole, a lift cap, and a plurality ofhoists of the primary lifting system.
 8. The method of claim 7, whereinthe lift cap is disposed at an axial end of the frusto-conical towersections, the plurality of hoists is disposed on an outer surface of thelift cap, and the lift pole is disposed within an inner volume of atleast one frusto-conical tower section.
 9. The method of claim 1,wherein a cross-section of each frusto-conical tower section in a planeparallel with a base of each frusto-conical tower section has apolygonal, circular, oval, corrugated, or fluted shape.
 10. A towerlifting system, comprising: a primary lifting system disposed at leastpartially internal to an inner volume of a first tower section of amulti-section tower, wherein the inner volume of the first tower sectionis defined by a wall of the first tower section, and wherein the primarylifting system is configured to raise the first tower section, asecondary lifting system, and the primary lifting system to an assembledposition; and the secondary lifting system, wherein the secondarylifting system is configured to raise the first tower section to alifting position.
 11. The system of claim 10, wherein the secondarylifting system comprises first hoists configured to raise the firsttower section to the lifting position from a tower foundation and mountsconfigured to secure the first tower section in the lifting position.12. The system of claim 10, wherein the primary lifting system comprisesa lift pole and a plurality of cables, wherein the lift pole isconfigured to lift the first tower section to the assembled position asthe plurality of cables are reeled in by second hoists.
 13. The systemof claim 10, wherein the primary lifting system is configured to supportand lift a nacelle of the tower, wherein the nacelle comprises a windturbine rotor, a wind turbine generator, or both.
 14. The system ofclaim 10, comprising a leveling sensor coupled to a control system,wherein the control system is configured to regulate operation of theprimary lifting system based upon feedback from the leveling sensor. 15.The system of claim 14, wherein the control system is configured toregulate operation of at least one hoist of the primary lifting systembased upon feedback from the leveling sensor.
 16. A system, comprising:a lift cap configured to be disposed on an axial end of a nestedplurality of tower sections, wherein the lift cap is configured tosupport a tower section of the nested plurality of tower sections to belifted, and the lift cap comprises a first plurality of hoists disposedon an outer surface of the lift cap; and a lift pole coupled to the liftcap, wherein the lift pole comprises a lifting mechanism configured tolift the lift cap, the lift pole, and the tower section to be liftedfrom within a previously lifted tower section of a plurality of nestedtower sections.
 17. The system of claim 16, wherein the liftingmechanism comprises a first plurality of pulleys disposed on a firstaxial end of the lift pole and a second plurality of pulleys disposed ona second axial end of the lift pole.
 18. The system of claim 17, whereineach of the first plurality of hoists comprises a respective cablerouted through at least one of the first plurality of pulleys and atleast one of the second plurality of pulleys, and wherein each cable isconfigured to couple to a respective lifting lug of the previouslylifted tower section.
 19. The system of claim 16, comprising a secondplurality of hoists disposed on an inner surface of the lift cap,wherein the second plurality of hoists is configured to raise the towersection to be lifted from a lowered position to a raised positionagainst the lift cap.
 20. The system of claim 16, wherein the lift capcomprises a plurality of wheels configured to travel along an outersurface of the previously lifted tower section as the lifting mechanismlifts the lift cap, the lift pole, and the tower section to be lifted.